1. Technical Field
The present invention relates generally to exhaust filtering and, in particular, to a filter system, regeneration system for the filter system, a combined soot removing system and applications of those systems.
2. Related Art
Filtering of exhaust is a well-known mechanism to reduce pollution. Related art devices have suffered from a number of drawbacks. For instance, most of the filters are adaptations of substrates used for automotive catalytic converters in which alternating channels are plugged to force the gas through the substrate walls. A number of other filter configurations and materials have been tried, but none have been robust enough or cost effective enough for widespread use. Also, once the particulates or other materials have been collected, they must be removed before the filter can function effectively. This is typically accomplished by igniting and burning the collected burnable particulates using a variety of techniques. Current techniques in the art of regeneration are expensive, complex, and many are outright hazardous, e.g., some use explosive, compressed gas or highly flammable (compared to diesel fuel) liquids.
In addition, the catalytic converter materials were designed to operate at much lower temperatures than can be reached during an uncontrolled regeneration (rapid, uncontrolled burning of the soot collected in the filter). In many cases, the filter media cracks, melts, or is otherwise damaged by either vehicle induced vibration or very high temperatures. In addition, many filters include two or more integral filter sections for filtering different pollutants. Unfortunately, these filters make regeneration difficult. Further, when one filter section is in need of repair, all of the sections must be replaced.
Another problem with related art devices is their inability to accommodate different applications because of their inflexible size. A new mold must be made for each different size filter unit, which dramatically increases cost or limits the ability to tailor the filter for the application. U.S. Pat. No. 5,250,094 to Chung et al. discloses a filter construction having a number filter sections 114. Unfortunately, the device is limited in application by the size of the enclosure.
Related art devices also do not adequately provide a regeneration system that is safe and controllable. In particular, U.S. Pat. No. 5,820,833 to Kawamura includes an electric wire net that is integral with a filter, i.e. in-filter regeneration. Since the regeneration system and filter are inseparable, the device may be subject to vibrations that may induce damage. U.S. Pat. No. 5,394,692 to Teuber-Ernst discloses a separate regeneration system that is fired by an explosive gas, which is an unsafe situation when in an environment where other fuel sources are nearby. Another problem with these regeneration systems is their inability to adequately control the rate of burn and, therefore, the temperature of the filter during regeneration. Many filters cannot withstand the repeated exposure to higher temperatures caused by some regeneration systems. Further, the potential for regeneration to proceed uncontrollably is potentially dangerous due to the extreme amount of heat that is generated by the burning soot.
Accordingly, there is a need in the art for a filter that includes separate filtering sections for ease of repair and regeneration. Furthermore, there is a need for a readily size-adjustable filter system. It would also be advantageous if this filter could be retrofitted to a variety of exhaust producing devices that exhaust a variety of different pollutants. Moreover, there is also a need for a safe and controllable regeneration system. A system that combines the above filter and regeneration system would also be advantageous.
The invention provides an exhaust filter system that serves as a particulate trap, a muffler, and a purifier as well as a regeneration system that is safe and controllable. The filter system design removes the structural load from the filter, while the regeneration system design eliminates most of the failure modes found in current regeneration systems. The invention provides for longer filter life; less complicated regeneration, less modification to an exhaust producing device for retrofitting, and much lower life cycle costs to the end user. In addition, the filter system can tolerate much higher temperatures than conventional filter systems thereby increasing the durability and use range of the filters.
In a first aspect of the invention is provided a filter system for removing soot from the exhaust of an exhaust producing device, the filter system comprising one or more self-contained, module, attachable units for varying the size of the filter system. Each unit includes: a housing; a particulate filter section positioned within the housing; and a nitrogen oxide filter section having a gas-impervious inner cylinder spaced within the particulate filter section and a nitrogen-oxide removing catalyst positioned within the inner cylinder. This aspect provides a dual pass filter system that has two separate sections. The number of units can be selected to match the type of exhaust producing device, exhaust source size, and expected operating profile. However, even an individual unit can function as a complete, dual-pass filter. In addition, the filter system may replace a muffler in many settings, which reduces costs to an end-user, and may be retrofitted without major modifications to a variety of exhaust producing devices. Further, unlike pure catalyst based filter systems, the filter system is not limited for use with a particular exhaust producing fuel, e.g., expensive low-sulfur diesel fuel.
A second aspect of the invention includes a regeneration system for an exhaust filter, the system comprising an electrically heated regenerator for producing heated gas to be passed through the filter to regenerate the filter. This aspect provides a safer and more easily controlled regeneration process. The system may be implemented separate from the exhaust producing device to prevent vibration induced damage or may be coupled to the device where the device is capable of moving, e.g., a motor vehicle.
A third aspect of the invention provides a soot removing system for an exhaust producing device comprising: a filter for removing soot from exhaust of the exhaust producing device; and a regeneration system having an electrically heated regenerator for producing heated gas to be passed through the filter to regenerate the filter. This aspect provides for a combined system having the above-described attributes of the filter and regeneration systems.
A fourth aspect of the invention includes a motor vehicle comprising: an engine for driving ground engaging members; an exhaust filter for removing soot from exhaust of the engine, the filter including one or more attachable units for varying the size of the filter; and an electrically heated regenerator for producing heated gas to be passed through the filter to regenerate the filter.
The foregoing and other features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention.